Heating And Hot Water System - Worcester WM 12 Installation And Servicing Instructions

9. Heating and Hot Water System

9.1 The appliance is suitable for connection to fully pumped
conventional indirect hot water systems utilising an indirect
double feed cylinder. This appliance is not suitable for use on
gravity systems.
9.2 The flow and return sockets are located at the top of the
appliance. From the inside of the property the flow pipe is on
the right hand side and the return pipe is on the left hand side.
9.3 There is no requirement for a system bypass.
9.4 The pressure jet burner fitted to the appliance has full auto-
matic control and hence there is no requirement for heat leak
radiators.
9.5 The appliance is suitable for connection to open vent or
sealed systems..
9.6 When the appliance is installed on a sealed system it is rec-
ommended that copper pipe is used; on open vent systems cop-
per or plastic pipe can be used.
9.7 The primary system should be flushed and treated in accor-
dance with the recommendations of BS 7593:1992 before the
system is handed over to the user.
9.8 A drain cock should be installed at the lowest point on the
heating circuit. The drain valve on the boiler (see fig. 2) is for
draining the boiler only.
9.9 The pump should be set in accordance with the heating load
requirements to give a flow and return differential temperature
of 11°C under full load conditions.
Open Vent Primary System.
(See Fig. 12).
The following points are for guidance only. The system installa-
tion should be carried out in accordance with BS 5449: Part 1.
1. Feed and Expansion System
The feed and expansion pipes must rise continuously from the
appliance and must be of the minimum diameter shown in
fig.12.
The cistern must be arranged to provide a minimum static head
Fig. 12. Typical fully pumped open vent system (Honeywell 'Y' plan).
Feed and
Vent Cistern
Heating vent
(22mm min.)
Boiler
Primary
S.H.
cold feed
(15mm min.)
150mm max
of 1 metre above the top of the highest point in the heating cir-
cuit.
2. Filling and Venting
Air in the appliance is expelled through the vent pipe or dissipat-
ed into the system. Manual air vents should be fitted at any high
points in the system.
Sealed Primary System
(See Fig.13 and 14).
The appliance is supplied with a manual reset thermostat and is
suitable for use with a sealed primary system.
General
The system should be installed in compliance with the require-
ments of BS5449: Part 1. The boiler must be fitted with a spring
loaded safety valve set to operate at 3 bar (45 psi) and the pipe
connections made throughout the system must be capable of
sustaining a pressure of up to 3 bar.
Manual air vents should be fitted at any high points in the system.
The following is a list of major items which must be fitted to the
system:
1. Safety valve – 3 bar
2. Pressure gauge – 0 to 4 bar.
3. Expansion vessel
4. Automatic air vent.
Domestic hot
water cylinder
Diverting
valve
Pump
12
S.H. – Minimum static head 1m (3ft)
measured from the highest point in the
heating system (top surface of the appliance
S.H.
or highest point in the heating system) to the
water level in the feed and expansion tank
N.B. A drain cock should be
installed at the lowest point of
the heating circuit
Radiator